The present invention generally relates to belt tensioners and more particularly to belt tensioners that can be easily and precisely installed in operative relation with a timing or drive belt.
Belt tensioners are well known in the prior art and have been used in many belt systems heretofore. A belt tensioner is a movable support structure that rotatably supports a portion of a belt in an engine or other mechanical system. A belt tensioner is movable to compensate for increases or decreases in belt path length due to wear and other factors to provide a constant belt tensioning force on a timing or drive belt.
A common type of conventional belt tensioner includes a fixed structure and a pivoted structure pivotally mounted on the fixed structure by a pivot assembly. The pivoted structure carries a belt-engaging pulley. A coil spring is mounted in surrounding relation to the pivot assembly and the ends of the spring are connected between the fixed and pivoted structures to bias the latter with respect to the former toward a position of maximum belt take-up. The spring biasing force decreases as the pivoted structure moves from a position of minimum belt take-up to a position of maximum belt take-up. Although the spring force varies within the range of movement provided, a substantially constant tension is maintained on the belt. The principles stated above can be appreciated from U.S. Pat. No. 4,473,362.
It is also known that when a belt tensioner is installed on an engine, the tensioner should be installed to apply a predetermined static tensioning force on the belt. On some belt tensioners, this is achieved by adjusting the same so that the pivoted structure that carries the pulley is positioned between two end stops that define the range of movement for the pivoted structure. A belt tensioner should maintain the proper belt tension level throughout the entire operational angular movement of the pivoted structure.
In accordance with prior art arrangements, during the adjustment or installation of the tensioner, an eccentric adjusting member forming part of the fixed structure is rotated to move an eccentric pivoted structure eccentrically disposed about the eccentric adjusting member. Rotating the eccentric adjusting member causes the eccentric pivoted structure to move into tensioning engagement with the belt. When the belt reaches a predetermined static tension, the opposing force upon continued rotation of the eccentric adjusting member causes the eccentric pivoted structure to move away from its stop in the belt engaging direction and into a position between the stops, wherein the belt tensioning pulley is disposed in a predetermined static tensioning relation to the belt. Such arrangements are proposed in U.S. Pat. No. 5,244,438, and UK Patent No. 2,249,152.
A shortcoming in the designs of these two patents is that they both disclose belt tensioners that provide an eccentric pivoted structure that is guided for movement on the eccentric adjusting member as the eccentric adjusting member is rotated to install the tensioner in tensioning relation with the belt. Thus, the eccentric pivoted structure and pulley mounted thereon follow a generally arcuate path when moving towards the belt and into tensioning engagement therewith. In addition, the spindle on which the pivoted structure is mounted and/or a base plate on which the eccentric adjusting member is mounted undergoes a connecting rod-type movement as the eccentric adjusting member is rotated. As a result of these movements, the base plate and/or pivot shaft may be installed out of alignment for proper tensioning of the belt when the mounting bolt is fixed and the eccentric adjusting member and pivot shaft are installed in there final, installed position.
U.S. Pat. No. 5,759,125 suggests a belt tensioner arrangement comprising a rigid support base having a longitudinal slot for allowing translational displacement of the support base to adjustably secure the support base to the vehicle engine. This movement is not restricted to an arcuate, connecting-rod type movement as with the two patents mentioned above, but is free to move in any direction as dictated by an externally applied force. This freedom of movement is no better or even worse than the connecting rod type arcuate movement with regard to proper alignment of the tensioner during installation. As with the two above-mentioned patents, the support base and/or pivot shaft in the '125 patent may be installed out of alignment for proper tensioning of the belt when the tensioner mounting bolt is eventually tightened and the tensioner is installed in its final position.